The present invention relates to a charged particle beam irradiation system for irradiating a charged particle beam onto a target and a method of beam irradiation; and, especially, the invention relates to a charged particle beam irradiation method and system in which the shape and intensity of the charged particle beam can be controlled in accordance with the three-dimensional shape of a target to be irradiated.
A charged particle delivery system is a system for forming a field for irradiation of a target by a charged particle beam in accordance with the three-dimensional shape of the target and for adjusting the distribution of the dose in the irradiation field.
Such a charged particle beam delivery system consists of a lateral direction beam shaping part for establishing an irradiation range in a plane perpendicular to the direction of the charged particle beam, and a trajectory direction beam adjusting part for adjusting the irradiation range in the direction of the charged particle beam (in the depth direction of the target). The lateral direction beam shaping part spreads the charged particle beam on a plane perpendicular to the direction of the charged particle beam and shapes the spread of the charged particle beam in accordance with the shape of the target projected on a plane perpendicular to the direction of the beam by cutting out the spread beam using a collimator. Further, the trajectory direction beam adjusting part adjusts the energy range of the charged particle beam in accordance with the cross-sectional shape of the target in the direction of the beam (in the depth direction of the target). A conventional charged particle beam delivery system of this type is disclosed on pages 2055-2122 of No. 8 (August, 1993) in Vol. 64 of "Review of Scientific Instruments".
For charged particle irradiation therapy, it is desirable to produce a conformal irradiation in which the irradiation is performed in accordance with the three-dimensional shape of a diseased part by irradiating a high dose of energy on the diseased part and a low dose of energy on parts other than the diseased part. As a conventional conformal irradiation method, a scanning method which scans a diseased part with a thin charged particle beam, a method of irradiating a diseased part with a charged particle beam by dividing the diseased part in layers using a multi-leaf collimator, etc. has been used. Japanese Patent Application Laid-Open 148277/1995 discloses a conformal irradiation method in which a beam is irradiated onto a diseased part by using a uneven ridge filter and a multi-collimator.
A conformal irradiation system using the scanning method becomes complicated since it is necessary to control the beam, as well as to measure the dose of the beam at a high speed and with a high accuracy. Also, a conformal irradiation apparatus using the method of irradiating a charged particle beam by dividing the diseased part in layers or the method using a uneven ridge filter becomes complicated since it is necessary to properly control a multi-leaf collimator with a required timing.